The Cannot Modify Sprite notice prevents me from saving, adding layers, opening new canvases, exiting the program, and every other option. I’m not sure how it started.
I was having the same issue just now but used a random trick I learned for when Photoshop locks up sometimes and hid all my layers. After I hid the layer I was working on I was able to save and exit. When I re-opened the project I was able to work normally.